A spin transfer torque MRAM (Magnetic Random Access Memory) using a perpendicular magnetization film as a recording layer is advantageous in reducing a write current and increasing the capacity. A magnetic stray field generated from a reference layer is generally larger in a perpendicular magnetization type MTJ element than in an in-plane magnetization type MTJ element. Also, the recording layer having a coercive force smaller than that of the reference layer is strongly affected by the magnetic stray field from the reference layer. More specifically, the thermal stability decreases under the influence of the magnetic stray field from the reference layer.
As a means for reducing the magnetic stray field from the reference layer, which affects the recording layer in the perpendicular magnetization type MTJ element, a structure including a field canceling layer having magnetization in a direction opposite to that in the reference layer, a dual-pin structure, and the like have been proposed. When the element size decreases, however, the influence of the variation in element size on a write current increases. That is, if the element size varies, the magnetic stray field cannot be decreased to zero any longer, and the variation in magnetic stray field increases the variation in write current.
Also, in an MTJ element, the resistance value of a tunnel insulating film about 1 nm thick is read out. This tunnel insulating film is very thin. This poses the problem that, e.g., the sidewall of the tunnel insulating film is damaged when processing the MTJ element, redeposition of a metal occurs and causes insulation breakdown, or the reliability of the tunnel insulating film deteriorates and increases the variation in read current.